This proposal is submitted in response to RFA DK-03-022 "Ancillary Studies to Obesity-Related Clinical Trials." We are making application to prospectively examine the cognitive effects of bariatric surgery in participants from the Longitudinal Assessment of Bariatric Surgery (LABS) project. There is growing evidence that obesity is associated with adverse neurocognitive outcome. Recent studies demonstrate that elevated body mass index (BMI) is an independent risk factor for Alzheimer's disease, structural brain abnormalities, and cognitive dysfunction in older adults. Preliminary work from our lab extends these findings and shows structural brain differences and cognitive dysfunction also exist in obese young and middle-aged adults. Bariatric surgery is increasingly viewed as an effective intervention for morbid obesity, though its effects on cognition are unknown. Post-operative nutritional deficiencies are common and can adversely impact cognitive performance. However, substantial weight loss resolves or improves many medical conditions with reversible cognitive effects, suggesting bariatric surgery may provide cognitive benefits. No study to date has examined the cognitive effects of bariatric surgery. To do so, the proposed study will prospectively assess cognitive performance in 125 bariatric surgery patients enrolled in the LABS project and 125 matched controls. Bariatric surgery patients will complete a computerized cognitive test battery at four time points: pre-operatively, 12weeks post-operatively, 12 months post-operatively, and 24 months post-operatively. Matched control participants will complete the test battery at similar intervals. Demographic, medical, and psychosocial information will be collected to elucidate possible mechanisms of change. We hypothesize that the substantial weight loss following bariatric surgery will be associated with improved cognitive performance. Findings from the proposed study will provide important information regarding: 1) the cognitive effects of bariatric surgery; 2) possible mechanisms for these effects; and 3) the contribution of cognitive performance to short- and long-term outcome of bariatric surgery. Determining these effects may impart key insight into the neurocognitive consequences of obesity and identify the most effective treatment options.